1. Field of the Invention
Aspects of the invention relate to a power conditioner for supplying power generated from a fuel cell or a solar cell to a power using point, and a method of managing the power controller.
2. Description of the Related Art
According to the related art, power generated by a fuel cell is supplied to a power using point through a power conditioner, as shown, for example, in FIG. 1. FIG. 1 shows a block diagram of a power conditioner disclosed in U.S. Patent Application Publication No. 2004/0219399 .Referring to FIG. 1, a direct current (DC) voltage of approximately 40 to 50V generated by a fuel cell 10 constituting a power source is boosted to a DC voltage of approximately 360 to 400V in a main converter 20. The fuel cell 10 has a structure in which a plurality of unit cells are stacked, and the DC voltage of 40 to 50V is outputted by adding together the voltage generated by each of the unit cells. The DC voltage boosted in the main converter 20 is transformed into an alternating current (AC) voltage in an inverter 30. The AC voltage is supplied to a power using point 40.
Power is required for controlling operations of various driving devices (blowers, motors, cooling fans, controllers, and the like), the main converter 20, and the inverter 30, and this power is provided by a DC voltage of approximately 20 to 30V that is obtained from an auxiliary converter 60. That is, a portion of the power boosted to the DC voltage of 360 to 400V in the main converter 20 is diverted to the auxiliary converter 60 to reduce the voltage to a DC voltage of approximately 20 to 30V, and the reduced voltage is supplied to the various driving devices, the main converter 20, and the inverter 30. The output voltage from the auxiliary converter 60 is also used for controlling the auxiliary converter 60. Elements in the fuel cell system that use a portion of the power generated by the fuel cell 10, such as controllers for controlling the main converter 20, the inverter 30, the auxiliary converter 60, and the various driving devices included in the fuel cell 10, are called balance-of-plant (BOP) elements 70. The term BOP elements will be used hereinafter to refer to these elements. The power conditioner also includes a battery 50 for use as a power source when a power supply to the auxiliary converter 60 is not stable, such as during an initial start-up mode of the fuel cell 10. The battery 50 is charged by the output voltage of the main converter 20 when the fuel cell 10 is in a normal operation mode, and is used as a power source for the auxiliary converter 60 when the fuel cell 10 is in an initial start-up mode. Power may also be supplied to the auxiliary converter 60 by connecting the auxiliary converter 60 to a source of household voltage, such as 110V or 220V, instead of using the battery 50. when the fuel cell 10 is operating in the initial start-up mode.
However, in the power conditioner described above, power to be supplied to the BOP elements 70 must pass through the main converter 20 and the auxiliary converter 60, resulting in an inevitable power loss due to the two voltage conversions that are performed. That is, as shown in the main converter 20 of FIG. 1, a voltage transformation proportional to a winding ratio between two windings W11 and W21 is performed. Power loss occurs during this voltage transformation because a portion of the power being transformed is converted into heat. In the same manner, a power loss occurs during the voltage transformation in the auxiliary converter 60. It is known that the power loss in the main converter 20 is approximately 10% and the power loss in the auxiliary converter 60 is approximately 20%. Accordingly, the power that is supplied to the BOP elements 70 after passing through the main converter 20 and the auxiliary converter 60 is approximately 70% or less of the power that is outputted from the fuel cell 10. In order to reduce the power loss, a portion of the power outputted from the fuel cell 10 can be directly supplied to the BOP elements 70 without passing through the main converter 20 and the auxiliary converter 60. However, the voltage outputted from the fuel cell 10 fluctuates according to the operating conditions of the fuel cell, that is, according to a load of the fuel cell 10. Accordingly, when the voltage outputted from the fuel cell 10 is directly supplied to the BOP elements 70, the operation of the overall system can be unstable.
In order to address the above problem, there is a need to develop a method of supplying stable power to the BOP elements 70 with a reduced power loss by reducing the number of voltage conversions that are performed.